The invention relates to a high-pressure discharge lamp comprising a translucent lamp vessel, and sealed in a vacuum-tight manner, which is filled with ionizable gas. Electrodes project into the lamp vessel and are connected to current supply conductors which extend to the exterior through the wall of the lamp vessel. The electrodes each comprise a rod of mainly tungsten, around which is wound at its end projecting inside the lamp vessel a wire portion of mainly tungsten, having ends with end faces. Such a lamp is known inter alia from British Patent Application No. 8,331,819 to which U.S. Pat. No. 4,594,529 corresponds.
The wire helically wound around the rod of electrode may have for its object solely to obtain a satisfactory temperature distribution over the electrode, but may also serve to hold electron-emitting material.
During the operation of helically winding the wire, the beginning part of the wire must be held, for example, in a clamp and after the operation of winding the wire has been accomplished, the wound wire portion must be separated from the remaining non-wound wire. The clamped beginning part of the wire must also be removed. The wound wire portion is freed from the non-wound beginning and end parts by clipping, pinching, grinding or cutting. Burrs are then formed mostly at the end faces of the wound wire portion. Due to the fact that the wound wire portion is freed, its ends spring out because they were deformed to a lesser extent during winding than parts remote from the ends. Moreover, it is not possible to approach the wound wire portion with the tools very closely, the less so if this wire portion must not be damaged. In high pressure discharge lamps manufactured in mass production, the ends of the helically wound wire portion therefore project for a considerable part beyond the sheath of the helical portion and the end faces have a burr.
However, projecting ends may be disadvantageous because they may form a preferential area at which the discharge arc can terminate or because upon ignition of the lamp they prevent the discharge arc from soon terminating on the tip of the electrode. They may also be disadvantageous if during manufacture of the lamp the electrodes must be slipped inside through a narrow opening of the lamp vessel.
The invention has for its object to provide a solution for the problem of projecting ends in discharge lamps comprising rods provided with a winding and to provide lamps having electrodes of a construction that can be manufactured in a simple manner.